Fig. 3. Interactions among drugs and target proteins offer chances for drug combination, co-administration, and repurposing.

Drug molecules may bind with off-target proteins that induce side effects (labeled by red arrows), which should be avoided. Though, the therapeutic drug molecules should be reserved, as they function as desired to cure diseases (labeled in green arrows). Interactions between drugs provide an opportunity for enhanced therapeutic performance through drug co-administration and combination (labeled by cyan arrow). Drug similarity conveyed by drug-target interactions provides a chance for drug repurposing (labeled by orange arrows). Drug targets may be expanded to similar proteins using protein-protein interactions for drug repurposing (labeled in purple arrows). Drug molecules in this figure include epinephrine (for “Drug 1”) and benzene (for “Drug 2”) as examples, using the icons from Biorender.